The present invention relates to a cooling high frequency power transistor, in which the heat of the power loss is at least partially conducted from a semiconductor material through a collector conductor.
High frequency power transistors that turn power loss into heat which is brought out through a collector conductor, include plastic box transistors. The power loss of these transistors is typically a few watts at the most. Ordinarily these transistors have collector, emitter and base conductors that radially extend from the box, which conductors are attached onto the surface of, e.g., a circuit board and not into the holes in the circuit board as electrical components are traditionally attached. The constructions of even higher power transistors and low frequency transistors are completely different from these high frequency power transistors.
One known solution to the cooling problem of a transistor of this kind involves placing the transistor into a metal socket formed for it, to which socket ceramic pieces are attached. The pieces insulate electrically but conduct heat in order to insulate the base and the collector of the transistor from ground potential and to conduct heat from the collector to the socket and then to dissipate the heat from the socket. The state of the art is illustrated in FIG. 1 where reference number 1 indicates the socket arrangement as a whole, and reference number 2 indicates the ceramic pieces made, e.g., of aluminum oxide or beryllium oxide, for electrical insulation and conduction of heat. Reference number 3 indicates copper elements for the attachment of the collector and the base of the transistor, and the attachment of an adjustment circuit to the collector. This metal socket 1 is then attached with its face 4, facing downward and away from the transistor, to a circuit board to which also a separate adjustment circuit of the high frequency power transistor is attached. The socket 1 takes this form both in order to dissipate the power loss directly from the surface of the socket to the surrounding environment to conduct heat, from its area, which is considerably larger than the collector of the transistor, to the circuit board which in turn conducts it to a wider area, e.g., to the ground area. Thus the heat is dissipated through the entire circuit board.
Another method of cooling a plastic box transistor of this kind involves using a ceramic material circuit board, instead of a plastic material board, which is usually made of glass fibre epoxy. Such a ceramic circuit board made of a substrate material that conducts heat considerably better than glass fiber apoxy, e.g., aluminum oxide.
The cooling methods presented above are efficient enough, but the one mentioned first is both complicated and difficult to construct. It is thus also an expensive solution. There are also problems connected with the latter method, including the lack of flexibly and reliably in coupling of the ceramic material to the larger surrounding circuit board and/or box. Even this solution is thus relatively expensive and difficult.